In the completion of wells built into the earth, a string of casing is normally run into the well and a cement slurry is flowed into the annulus between the casing string and the wall of the well. The cement casing slurry is allowed to set and form a cement sheath which bounds the string of casing to the wall of the well. Perforations are provided through the casing and a cement sheath adjacent the sub-surface formation. Fluids, such as oil or gas, are produced through these perforations into the well.
Hydraulic fracturing is widely practiced to increase the production rate from such wells. Fracturing treatments are usually performed soon after the formation interval to be produced is completed, that is, soon after fluid communication between the well and the reservoir interval is established. Wells are also sometimes fractured for the purpose of stimulating production after significant depletion of the reservoir.
Hydraulic fracturing techniques involve injecting a fracturing fluid down a well and into contact with the subterranean formation to be fractured. Sufficiently high pressure is allowed to the fracturing fluid to initiate and propagate a fracture into the subterranean formation. Proppant materials are generally entrained in the fracturing fluid and are deposited in the fracture to maintain the fracture open.
Several such hydraulic fracturing methods are disclosed is U.S. Pat. Nos. 3,965,982; 4,067,389; 4,378,845; 4,515,214; and 4,549,608 for example. It is generally accepted that the in-situ stresses in the formation at the time of such hydraulic fracturing generally favor the formation of vertical fractures in preference to horizontal fractures.
Wells completed through formations at multiple intervals always present a challenge for effective treatment. Frequently, various methods of zone isolation or diverting will be used in treating more than one well, especially if the zones of interest are separated by a few hundred feet. Wells which are perforated over several hundred feet in a single zone also create a challenge to treat effectively with well stimulation such as acidizing or hydraulic fracturing.
Therefore, what it is needed is a method for hydraulically fracturing a formation having multiple intervals or zones which method does not require zone isolation.